投稿时间：2018-08-03
修订日期：2019-01-19
网络发布日期：2019-07-03
中文摘要:木落寨矿床位于川西冕宁-德昌稀土成矿带的北部，郑家梁子矿段是该矿床的主要成矿段。野外勘查发现，郑家梁子矿段主要的赋矿岩石是大理岩，其中发育的张性断裂充填大量矿脉，与矿带中其他矿床以正长岩为赋矿围岩的特征明显不同，而大理岩是否是成矿物质的主要来源尚不清楚。为进一步明确大理岩、正长岩和稀土物质来源之间的关系，文章对相关岩石和矿石进行地球化学特征对比分析。正长岩全岩稀土元素含量为1211×10-6~2974×10-6，稀土元素配分曲线呈轻稀土元素富集，重稀土元素亏损的特征。近矿蚀变大理岩稀土元素配分曲线整体呈右倾，稀土元素总量为1131×10-6~1935×10-6，而远矿新鲜大理岩稀土元素总量为8.20×10-6~8.69×10-6，由此可见，大理岩很可能不是稀土物质的主要来源。新鲜大理岩的δ13CV-PDB变化范围为1.3‰~1.6‰，δ18OV-SMOW介于23.2‰~23.7‰之间，显示其是海相碳酸盐岩变质的产物，蚀变大理岩的δ13CV-PDB变化范围为0.4‰~0.7‰，δ18OV-SMOW介于15.7‰~16‰之间，显示其受热液蚀变影响，并经历碳酸盐的溶解作用。新鲜大理岩与蚀变大理岩的δ13CV-PDB值变化较小（0.4‰~1.6‰），说明这2种大理岩为同源，近矿大理岩可能只是碳酸盐岩溶解蚀变的产物。矿脉中的方解石δ13CV-PDB变化范围为-4.6‰~-4.7‰，δ18OV-SMOW介于11.8‰~12.5‰之间，显示出碳酸岩岩浆经历低温蚀变的过程，证明矿脉与大理岩没有明显物质来源关系。矿石中氟碳铈矿的206Pb/204Pb、207Pb/204Pb与208Pb/204Pb分别为18.3143~18.3629、15.6243~15.6349和38.6197~38.7309，正长岩的206Pb/204Pb、207Pb/204Pb和208Pb/204Pb分别为18.3233~18.3568，15.6298~15.6360和38.6664~38.6880。正长岩和氟碳铈矿的铅同位素特征一致，显示稀土的物质来源很可能是正长岩或隐伏的碳酸岩。本次研究选取典型矿石中与氟碳铈矿密切共生的金云母进行Ar-Ar同位素定年。鉴于矿石中的云母和氟碳铈矿并不存在多期次性，研究测得该矿段金云母的40Ar/39Ar坪年龄为（27.6±0.2） Ma，可以很好地代表成矿时代。
Abstract:The Zhengjialiangzi ore section is the main metallogenic block of Muluozhai deposit which is located in the northern part of the Mianning-Dechang REE metallogenic belt in western Sichuan. It is found that the main orebearing rock in the Zhengjialiangzi ore block is marble, in which the developed tensile faults fill a large number of veins through field investigation. As the ore-bearing surrounding rock in Zhengjialiangzi ore block, the marble is obviously different from the other deposits'surrounding rock-syenite in the ore belt. In order to further clarify the relationships between marble, syenite and REE source, this study conducted comparative analyses of the geochemical characteristics of related rocks and ores. The REE content of syenite is 1211×10-6~2974×10-6, and the REE distribution curve is characterized by light rare earth element enrichment and heavy rare earth element depletion. The near-mineral alteration marble has a right-dip REE distribution curve, and the total REE content is 1131×10-6~1935×10-6, while the total REE content of fresh far marble away from the ore body is 8.20×10-6~8.69×10-6, which shows that fresh marble may not provides a source of rare earth materials. The δ13CV-PDB of fresh marble varies from 1.3‰ to 1.6‰, and the δ18OV-SMOW ranges from 23.2‰ to 23.7‰. It shows that the fresh marble is the product of metamorphism of marine carbonate. The variation of the δ13CV-PDB of altered marble is 0.4‰ to 0.7‰, and the δ18OV-SMOW is between 15.7‰ and 16‰, which indicates that the marble is affected by hydrothermal alteration and underwent carbonate dissolution. The changes of δ13CV-PDB values of fresh marble and altered marble are small (0.4‰~1.6‰), indicating that these two marbles are homologous. Near-mineral marble may be only a product of dissolution and alteration of carbonate rocks. The range of δ13CV-PDB of calcite in the vein is -4.6‰ to 4.7‰, and δ18OV-SMOW is between 11.8‰ and 12.5‰, which shows that the carbonate magma undergoes low temperature alteration, which proves that the vein and marble are not. The 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb values of bastnaesite in ore are 18.3143~18.3629, 15.6243~15.6349 and 38.6197~38.7309. The 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb values of syenite is 18.3233~18.3568, 15.6298~15.6360 and 38.6664~38.6880. The comparison shows that the Sr-Nd-Pb isotope data of the syenite and carbonate in the three deposits are close, and it is likely that they are from the same syenite-carbonate complex. The existing diagenesis and metallogenic ages of the Muluozhai deposit are different due to the different testing methods and test minerals. In this study, phlogopite, which is closely co-existing with bastnaesite, was used for the Ar-Ar determination. In view of the fact that the phlogopite and bastnaesite do not have multiple stages in the ore, the age of the formation of phlogopite (27.6±0.2) Ma is a good representative of the metallogenic age.
keywords:geology metallogenic characteristics geochemistry material source 40Ar/39Ar age Zhengjialiangzi ore block
文章编号：
中图分类号：P618.7
文献标志码：
基金项目:本文得到国家自然科学基金面上项目（编号：41772044）、中国地质科学院基本科研业务费（编号：YYWF201509、YYWF201705）和中国地质调查局地质调查项目（编号：DD20190060）联合资助
引用文本：
付浩邦,刘琰,郑旭,贾玉衡,丁岩.2019.川西木落寨稀土矿床年代学、地球化学与成矿特征[J].矿床地质,38(3):491~508FU HaoBang,LIU Yan,ZHENG Xu,JIA YuHeng,DING Yan.2019.Geochronology, geochemistry and metallogenic characteristics of Muluozhai deposit in southwestern Sichuan Province[J].Mineral Deposits38(3):491~508
图/表
